Diagnosing disease or injury of the lower extremities is challenging due to the complex anatomy of the lower leg, ankle, and foot. Medical imaging techniques, such as x-ray, magnetic resonance imaging (MRI), computed tomography (CT), fluoroscopy, and ultrasound provide images of soft tissue, bone, and vasculature that are useful in diagnosing illnesses and injuries in the lower extremities. Images are used to evaluate a patient's knee, ankle or foot for a wide range of problems, including fracture, fusion of joints, arthritis, joint degeneration, localization of a foreign body, determination of chronic pain, and the like.
Body positioning is important in obtaining specific planar views in imaging the lower extremities. Because the anatomy of the lower extremities is complex, evaluation of an image of the area is improved by specific positioning the knee, ankle, and foot during the creation of the image. Depending on the nature of the problem, an injury to the ankle may be evaluated using an image of the foot in either dorsiflexion (toe pointed up) or plantar flexion (toe pointed down). Patients are routinely scanned with the ankle in about 10 degrees to about 20 degrees of plantar flexion. Such a position is generally more comfortable for the patient and provides more consistent visualization of lateral ligamentous anatomy.
Depending on the illness or injury, a foot may be imaged in the oblique axial plane (i.e., parallel to the long axis of the metatarsal bones), oblique coronal plane (i.e., perpendicular to the long axis of the metatarsals), and/or oblique sagittal plane. Ankle imaging includes axial, coronal, and sagittal planes. For tendon abnormalities, the ankle may be positioned to provide an image of the tendons across the malleoli.
The simultaneous scanning of both lower extremities provides comparative images to aid in the diagnosis of injuries or illnesses. By scanning both normal and injured extremities, the images of the structures may be compared. Such simultaneous scanning is useful in evaluating tendon or ligamentous disorders, where the extremities are positioned at nearly the same angle of inflection for comparison.
Specific disorders of the lower extremities are routinely imaged in predetermined positions for assessment. For example, for subtalar (rotational) instability, coronal imaging is performed with the ankle placed in a plantar flexion position; in identifying subluxation (misalignment) of the bony joint or peroneal tendons, an axial image is obtained with the ankle in a dorsiflexion position. Evaluation of partial tears of the tendons and ligaments, as well as verifying anterior and posterior bony displacement routinely require the need for sagittal reconstructions to accentuate the fat plane between the tendons and to allow better visualization of joints and ligaments.
Medical imaging techniques currently require that a patient remain motionless in a specific position during the imaging. For lower extremity imaging, a patient must maintain one or both ankles at a predetermined angle. Depending on the image desired, a scan might take from about 10 to about 15 minutes per view (axial or coronal). Maintaining a given position without moving for that length of time proves difficult for many patients. In order to assist a patient in maintaining the desired angle for imaging one or both of the lower extremities, pillows or cushions are sometimes placed under the patient's knees. Such methodologies usually result in difficult to reproduce positioning, slippage, and non-standardized angles of flexion.
Some imaging facilities attach the pillow or cushion to the patient, for example, by using surgical tape, to attempt to maintain the patient in the correct position and reduce slippage. When patients are unable to relax the ankle to allow the foot to rest flat when the knee is bent, some imaging facilities immobilize such patients by taping the patient's toes to the table to create the angle and prevent slippage.
Patients that present with an illness or injury to the lower extremity are usually in pain, and do not tolerate medical imaging positioning well for long periods of time. Movement during imaging results in poor diagnostic quality and necessitates repeated imaging, which is a burden to the patient as well as causing scheduling problems in busy imaging centers. Repeat images also adds to the amount of radiation to which the patient is exposed. Removal of tape is often painful for a patient. Accordingly, a need exists for improved positioning devices and methods.